Methane extraction method and apparatus using high-energy diode lasers or diode-pumped solid state lasers

ABSTRACT

A method and apparatus for extracting methane gas from methane hydrate. The method includes heating the methane hydrate with a laser apparatus. The laser apparatus includes a diode laser or a solid state laser that is pumped with a diode laser. The laser is guided to a working end of a tool with a fiber optic bundle. The tool is guided to heat the methane hydrate with the laser, which emanates from a beam expander at the working end of the tool. The tool can be modified for removing obstructions of methane hydrate in pipelines. Also, the tool can be modified for extracting methane from mined methane hydrate, which is in a container. The characteristics of diode lasers or diode-pumped solid state lasers such as efficiency, size, nature of operation, environmental impact and durability, make methane gas extraction from methane hydrate economically feasible.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.provisional application No. 60/800,408, which was filed on May 16, 2006and which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates in general to a method and apparatus for methaneextraction, and more particularly, to a method and apparatus forextracting methane from methane hydrate using high-energy diode lasersor solid state lasers that are pumped with diode lasers.

BACKGROUND OF THE INVENTION

At various locations around the world, there are large supplies ofmethane gas in the solid, frozen form of methane hydrate. Beneath theocean bed, at various depths, methane hydrate deposits are estimated atmany trillions of cubic meters. Currently, there is no cost-effectivemethod of extracting methane from methane hydrate. However, as the costof energy increases, extraction of methane from methane hydrate maybecome cost-effective. However, there is a need for an efficient methodof extracting the methane from the methane hydrate.

Several proposals for extraction have been put forth. These includethermal stimulation, depressurization, and the use of chemicals, orinhibitors. However, currently proposed methods have various drawbacksthat reduce their cost-effectiveness. Currently, none of these methodsis considered to be commercially viable.

In particular, it has been proposed to use a chemically pumpedoxygen-iodine energy transfer laser (COIL) to thermally stimulate themethane hydrate. However, such a method would require large storagestructures for the chemicals that fuel the laser. Also, exhaust from thelaser would create a significant environmental hazard. Therefore, largescale scrubbing equipment would be required. Further, current COILsoperate continuously for only a few minutes, which is insufficient forlarge-scale methane extraction.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIG. 1 is a schematic block diagram of a vertical methane gas extractionoperation using a high energy semiconductor laser or a solid state laserthat is pumped with a semiconductor laser according to the presentinvention;

FIG. 2 is an enlarged schematic block diagram of a self-cleaning beamexpander of the apparatus of FIG. 1;

FIG. 3 is a schematic block diagram of a vertical methane gas extractionoperation using a high energy semiconductor laser or a solid state laserthat is pumped with a semiconductor laser according to a furtherembodiment of the present invention;

FIG. 3A is a cross sectional schematic view taken along the planeindicated by line 3A-3A in FIG. 3;

FIG. 4 is a schematic diagram of a horizontal drilling operation using asemiconductor laser tool for extracting methane gas from a methanehydrate deposit;

FIG. 5 is a schematic block diagram showing removal of a methane hydrateobstruction in a gas pipeline with a high energy laser tool that employsa high energy semiconductor laser or a solid state laser that is pumpedwith a semiconductor laser;

FIG. 6 is a schematic block diagram showing a laser drill forming a borein a methane hydrate formation;

FIG. 7 is a schematic block diagram showing a laser tool heating methanehydrate stored in a container.

FIG. 8 is a schematic block diagram showing a fiber-coupled diode laser;and

FIG. 9 is a schematic block diagram showing a fiber laser that is pumpedby fiber-coupled diode lasers.

SUMMARY OF THE INVENTION

Basically, the present disclosure concerns a method and apparatus forextracting methane gas from methane hydrate. The method includes heatingthe methane hydrate with a laser beam of a high energy diode laser or asolid state laser that is pumped with a diode laser to release methanegas from the methane hydrate. The end of the tool is placed in themethane hydrate, and the laser is guided with an optic fiber to the endof the tool.

Preferably, the laser beam is produced with a diode laser, which is moreefficient.

The laser can be operated in a pulsed mode or a continuous mode.

In a further embodiment, the invention includes a method of removing amethane hydrate obstruction in a gas pipeline by heating the methanehydrate with a laser beam of a diode laser or a laser that is pumpedwith a diode laser to change the phase of the obstruction.

In a further embodiment, the invention includes a method of boringthrough a methane hydrate formation to access a natural gas pocket thatis located beneath the methane hydrate formation. The boring methodincludes forming a bore hole through the methane hydrate with a laserbeam of a diode laser or a solid state laser that is pumped with a diodelaser and placing a conventional drill in the bore hole to drill beneaththe methane hydrate formation to form a second bore, which leads intothe gas pocket.

The invention includes an apparatus for extracting methane from methanehydrate. The apparatus includes an extraction tool; a diode laser or asolid state laser that is pumped with a diode laser; and an optic fiberfor leading a laser beam generated by the laser to a working end of theextraction tool.

The apparatus may further include a conduit for conducting extractedmethane from a methane formation toward a proximal end of the extractiontool.

The apparatus may further include a beam expander for expanding thelaser beam before the laser beam strikes the methane hydrate.

The apparatus may further include apparatus for forming an air curtainadjacent to a lens of the beam expander so that the lens isself-cleaning.

The apparatus may further include an air passage for delivering air tothe air curtain.

The extraction tool may include a water cooling passage for cooling theoptic fiber.

The extraction tool may be supported by a platform, which carries thehigh energy diode laser or diode-pumped solid state laser, its powersource and thermal management system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a methane extraction apparatus performing a verticalextraction operation in a body of water 101. A platform 102 is locatedat the water level of the body of water 101, such as the ocean. Beneatha crust 107, which forms the floor of the body of water 101 is a layer,or strata, of methane hydrate 108. An electric power plant 103 islocated on the platform 102. A high-power laser 104 (diode laser orsolid state laser that is pumped by a diode laser) is located on theplatform as shown. Although FIG. 1 shows an extraction operation onwater, the extraction can take place on dry land or ice with a drillingrig (not illustrated) that includes equipment similar to that located onthe platform 102.

Extending from the platform 102 to the methane hydrate strata is a laserextractor tool 113, which includes a laser light-carrying optic fiberbundle 109, a laser head assembly 114 and a conduit 105, fortransporting gas mixture 112 (methane and steam) to the platform 102.The extractor tool 113 is formed by concentric pipes, as shown. Theconduit 105 is formed between the inner surface of an outer pipe and theouter surface of an inner pipe. The gas mixture 112 is delivered to agas separator apparatus 106, which separates methane from steam andstores the separated methane in gas, liquid or solid form, as desired.Although not illustrated in FIG. 1, apparatus for cooling the fiberbundle is incorporated in the laser tool 113.

The laser head 114 can include a self-cleaning beam expander 110 fromwhich an expanded laser beam 111 is projected. The laser beam 111interacts with the solid methane hydrate 108 and causes a phase change.That is, the laser beam 111 heats the methane hydrate 108 and convertsthe methane hydrate into steam and methane gas. The beam expander 110increases the diameter of the laser beam, which increases the area ofthe methane hydrate 108 to be heated, which facilitates large scaleproduction of methane gas.

In the example of FIG. 1, the methane hydrate is located below a crust107 of the earth. Prior to the extraction process illustrated in FIG. 1,a bore is drilled through the crust 107 with a conventional drill (notillustrated). The well can then be capped until the extractor tool 113is inserted. The extractor tool 113 may be equipped to break a cap on acapped bore; however, such equipment is not illustrated.

FIG. 2 shows the self-cleaning laser beam expander 110 in more detail.The fiber bundle 109 is coupled to the beam expander 110 as shown. At alight exit lens of the beam expander 110 is an air curtain 204. Althoughit is not required to employ a self-cleaning beam expander, it isconsidered advantageous to maintain high production rates by reducingequipment maintenance and idle time.

Conventional equipment such as valves and pumps to control the pressureand flow inside the conduit 105 are not illustrated for simplicity.However, such equipment is well understood to those in the field of gasdrilling and will not be described here.

To minimize the loss of laser energy, it is preferred to minimize theseparation between the beam expander 110 and the solid methane hydrate.That is, it is desired to minimize the size of the gas pocketsurrounding the end of the extractor tool 113. Horizontal drilling canfacilitate positioning the end of the drill to minimize the gas pocketand the separation distance.

The laser 104 is a high-power semiconductor laser, or diode laser, whichis very efficient. In this application, “high power” means approximatelyone hundred kilowatts or more. Alternatively, the laser 104 can be asolid state laser that is pumped with a diode laser. Such lasers areparticularly suitable for methane extraction from methane hydratebecause of their extended on-time (time of continuous operation),durability, efficiency, size, power requirements, and maintenance andsupply requirements. For example, the life-expectancy of diode lasers orsolid state lasers that are pumped with diode lasers is approximately afew years, which is favorable for methane gas extraction, and diodelasers or solid state lasers that are pumped with diode lasers requireonly electricity to operate, which is favorable for methane gasextraction. Further, diode lasers or solid state lasers that are pumpedwith diode lasers do not produce waste materials at the work site.Therefore, diode lasers or solid state lasers that are pumped with diodelasers have little environmental impact on drilling sites.

The characteristics of diode lasers or solid state lasers that arepumped with diode lasers make them particularly suitable for extractingmethane from methane hydrate. Prior to this disclosure, methaneextraction from methane hydrate was generally considered to beuneconomic. However, the present method and apparatus is consideredlikely to render methane extraction from methane hydrate a commerciallyviable operation.

It is preferred that the laser beam of the methane extraction apparatusis a diode laser. Diode lasers currently have an efficiency ofapproximately 55-80%. Such relatively high efficiencies are required foreconomic methane gas production. The efficiency discussed herein is theso-called wall-plug efficiency, which is the energy in the output beamdivided by the energy input to the laser.

As used in this application, the phrase “solid state laser pumped with adiode laser” refers to a laser that uses a gain medium that is a solid,rather than a liquid or a gas, and is pumped with laser diodes.Currently, such lasers have efficiencies of approximately 10-20%.

A fiber laser is one type of solid state laser that is pumped with diodelasers. In a fiber laser, the optical fiber core serves as the medium.Currently, fiber lasers have an efficiency of approximately 30-35%.

The term “solid state laser” includes diode lasers, fiber lasers, androd or slab lasers.

Diode lasers are generally considered separately from diode-pumpedlasers. Thus, in this application, the terms “diode laser” and“diode-pumped laser” refer to separate types of lasers. That is, in thisapplication, the term “diode laser” excludes diode-pumped lasers.

Most preferably, the laser 104 is a diode laser, which more efficientthan lasers that are pumped by diode lasers. Assuming an average overallefficiency of an electricity generator to be approximately 40%, theratio of energy in extracted methane to energy input is expected to beapproximately 3 to 5 for a diode laser. Co-generating power plants,which generate both power and heat, have higher overall efficiencies(50-70%) and would improve the energy ratio.

Diode lasers or diode-pumped solid state lasers require no supplies ofchemicals or fuel other than electricity, which can be produced at thedrilling site. The electricity can be generated from a fraction of themethane gas produced by the well or from another energy source. Incontrast, for example, a COIL requires chemical supply tanks, whichgreatly increase the size and cost of the platform and associatedequipment. A diode laser or a diode-pumped solid state laser requiresonly electricity and is thus more compact and less costly. Thus, adrilling rig that uses a diode laser or a diode-pumped solid state laseris more cost effective and can tip the balance of an operation thatwould otherwise be economically unsound toward commercial viability.

Commercially viable gas production would require a laser that operatescontinually for relatively long periods of time. COILs, for example, canoperate for only short periods of a few minutes, which is insufficientfor economic gas production. A diode laser or a diode-pumped solid statelaser can operate for sustained periods that render methane extractionby the method disclosed above economically sound.

It is contemplated that the laser 104 will be operated in either of apulsed mode and a continuous mode. The pulsed mode may be advantageousfor breaking ice, which is the naturally occurring state of methanehydrate.

The beam parameter product (BPP) of a laser beam is defined as theproduct of beam radius (measured at the beam waist) and the beamdivergence half-angle (measured in the far field). The usual units aremm mrad (millimeters times milliradians). The BPP is often used tospecify the beam quality of a laser beam: the higher the beam parameterproduct, the lower the beam quality. Although there is equipmentavailable for improving the beam quality of laser beams, the beamquality is not an important consideration in heating methane hydrate.Thus, high beam quality (low BPP) is not required, which reduces thecosts.

FIGS. 3 and 3A show a vertical extraction tool 302 including an airconduit 309 and a water cooling passage 308. In the embodiment of FIG.3, an extraction is shown in a body of water 301. The extraction tool302 includes a conduit 306 for carrying extracted methane and steamtoward a platform, which is not illustrated in FIG. 3 but is like theplatform shown in FIG. 1. Beneath a crust 305 is a layer of methanehydrate 304. An expanded laser beam 303 heats the methane hydrate 304 torelease steam and methane gas.

As shown in FIG. 3A, optical fibers 320 are located within a coolingpassage 308 of the extraction tool 302. Cooling water is pumped into thecooling passage 308 through an input passage 307. The cooling water isdischarged through an output passage 310. The locations of the inputpassage 307 and output passage 310 are arbitrarily selected and are notnecessarily as shown.

The apparatus of FIG. 3 includes a beam expander 203 as shown in FIG. 2.Located within the cooling passage 308 is the air conduit 309 forsupplying air to the self-cleaning expander 203. As shown in FIG. 2, theair, which is under pressure, is used to form an air curtain 204 forcleaning an outer surface or lens of the beam expander 203.

FIG. 4 shows a horizontal drilling operation that on a body of water401. For simplicity, the platform and associated equipment is notillustrated. A horizontal extraction tool 402 extends from the platformand through an opening in the crust of the earth 405. The distal end ofthe horizontal extraction tool 402 is located in a layer of methanehydrate 404. An expanded laser beam 403 converts the methane hydrate 404into steam and methane gas as in the method illustrated in FIG. 1.

A mixture of steam and methane hydrate is conducted through a conduit inthe horizontal extraction tool 402 to a separator, as in the method ofFIG. 1. The horizontal drilling method is advantageous in that the tool402 can be moved along the length of the layer of methane hydrate 404 byextending the tool 402 in the horizontal direction to increaseproduction. Thus, horizontal movement extends the reach of the tool 402within a horizontal layer of methane hydrate 404 to increase theefficiency of gas production.

In another embodiment, as shown in FIG. 5, a laser tool 502 can be usedto remove a methane hydrate blockage, or formation, 504 in a natural gaspipeline or a methane gas and steam carrying pipeline 501. In coldclimates, methane hydrate formations 504 can cause obstructions in suchpipelines. The laser tool 502 includes a beam expander 203 like thatshown in FIG. 2. A laser beam is directed to the beam expander throughoptic fibers (not illustrated in FIG. 2). Through an opening in thepipeline 501 (not illustrated) the tool 502 is guided to an obstructionof methane hydrate. The expended laser beam 503 is then used to heat themethane hydrate 504, which converts the methane hydrate to steam andmethane gas thus removing the obstruction. As in the first embodiment,the laser used in this embodiment is a diode laser or a solid statelaser that is pumped by a diode laser.

As shown in FIG. 6, in another embodiment, a laser head drill 602 can beused to form a bore in a layer of methane hydrate 604 so that aconventional well drill can reach a pocket of natural gas 610 that islocated below the methane hydrate layer 604. The laser head drill 602incorporates a laser light-carrying fiber bundle, and a laser headassembly that includes a self-cleaning beam expander, like that shown inFIG. 2. The laser head drill 602 includes a conduit for carrying methanegas and steam away from a bore 606. As in the first embodiment, thelaser beam 603 heats the methane hydrate 604 and converts the solidmethane hydrate 604 to methane gas and steam, which is carried awaythrough the conduit in the laser head drill 602. As in the firstembodiment, the laser used in this embodiment is a diode laser or asolid state laser that is pumped by a diode laser.

Initially, a conventional drill is used to form a bore through a firstcrust layer 605. Then, the laser head drill 602 is deployed in the boreformed by the conventional drill to form the bore 606 through themethane hydrate layer 604. Then, a conventional drill is used again tobore through a second crust layer 607 to reach the pocket of natural gas610.

In a further embodiment, as shown in FIG. 7, a laser tool 702 can beused to extract methane gas from methane hydrate 704 that has been minedand is located in a container 701. The laser tool 702 is preferablymovable horizontally and vertically to optimize the reach of the tool702. In this embodiment, the expanded laser beams 703 heat the methanehydrate 704 to release methane gas 705 from an opening in the container701, as shown. As in the first embodiment, the laser used is a diodelaser or a solid state laser that is pumped with a diode laser. Also, asin the first embodiment, the laser tool 702 includes a bundle of opticfibers for carrying the laser beam from the laser to a beam expander atthe distal end of the tool 702.

Water 706 will collect in the container 701 as a result of the heat fromthe laser beams 703. Thus, in this embodiment, a separator may not berequired to separate steam from the methane gas 705. Since methane gasis lighter than steam, it will collect at the top of the container 701.Also, since methane gas exits the container through the opening in thecontainer, it is not necessary to form a conduit in the laser tool 702for conducting methane gas.

FIG. 8 shows a diode laser, which is the preferred type of laser for thelaser 104 or the source laser of any of the illustrated embodiments.FIG. 8 illustrates a known fiber-coupled diode laser module 812. Theelectrical power plant 103 is coupled to the laser module 812 by a cable810. Although FIG. 8 shows only two laser diode bars 816 any number oflaser diode bars 816 may be arranged in the laser module 812 dependingon the circumstances and output needs. In the illustrated embodiment,one cooling channel 814, which carries coolant, is associated with eachlaser diode bar 816. However, any number of cooling channels may bearranged in various configurations as long as heat is transferred fromthe diode laser bars.

As shown in FIG. 8, a pair of lenses 818 direct laser light to couplingand conditioning optics 820. For example, the coupling and conditioningoptics can include a containing lens, half-wave plates, beam compressionprisms, a polarization beam combiner, and spatial filters. A fiber portcoupler 822 couples the coupling and conditioning optics 820 to a fiber824. Laser light 826 emanates from the end of the fiber 824. Dependingon the capacity, a bundle of fibers 824 may be employed.

FIG. 9 shows an alternative known fiber laser that may be used as thelaser 104 in FIG. 1 or as the source laser in any of the illustratedembodiments. In FIG. 9, a master oscillator laser 910, which may be anyof several types of known lasers, is coupled to an optical fiber 912. Afiber-coupled diode laser pump 914 is coupled to a light coupler 916, asillustrated. Within the laser pump 914 is an array of diode lasermodules, such as that illustrated in FIG. 8, each of which is coupled toone of the illustrated optical fibers extending between the laser pump914 and the light coupler 916.

Downstream from the light coupler 916 is an active fiber 918 that isbeing pumped by the fiber-coupled diode laser modules. Furtherdownstream from the active fiber 918 are beam shaping optics 924. Laserlight 926 emanates from the beam shaping optics 924 or a fiber coupledto the beam shaping optics 924.

The apparatuses and methods discussed above and the inventive principlesthereof are intended to and will alleviate problems with conventionalmethane extraction methods and apparatuses. It is expected that one ofordinary skill given the above described principles, concepts andexamples will be able to implement other alternative procedures andconstructions that offer the same benefits. It is anticipated that theclaims below cover many such other examples.

1. A method of extracting methane gas from methane hydrate comprisingheating the methane hydrate with a laser beam of a diode laser or asolid state laser that is pumped with a diode laser to release methanegas from the methane hydrate.
 2. The method of claim 1 including;guiding the laser beam with an optic fiber to and end of a tool; andplacing the end of the tool in the methane hydrate.
 3. The method ofclaim 1 including expanding the laser beam with a beam expander at theend of the tool.
 4. The method of claim 1, wherein the laser is a diodelaser.
 5. The method of claim 1 including operating the laser in apulsed mode.
 6. The method of claim 1 including operating the laser in acontinuous mode.
 7. A method of removing a methane hydrate obstructionin a gas pipeline comprising heating the methane hydrate with a laserbeam of a diode laser or a solid state laser that is pumped with a diodelaser to change the phase of the obstruction.
 8. The method of claim 7including: providing a tool for supporting an optic fiber; and directingthe laser beam with an optic fiber toward a working end of the tool; andguiding the tool to direct the laser beam toward the obstruction.
 9. Amethod of boring through a methane hydrate formation to access a naturalgas pocket that is located beneath the methane hydrate formationcomprising: forming a bore hole through the methane hydrate with a laserbeam of a diode laser or a laser that is pumped with a diode laser; andplacing a drill in the bore hole to drill beneath the methane hydrateformation to access the natural gas pocket.
 10. An apparatus forextracting methane from methane hydrate comprising: an extraction tool;a diode laser or a laser that is pumped with a diode laser; and an opticfiber for leading a laser beam generated by the laser to a working endof the extraction tool.
 11. The apparatus of claim 10 further comprisinga conduit for conducting extracted methane from a methane formationtoward a proximal end of the extraction tool.
 12. The apparatus of claim10 further comprising a beam expander for expanding the laser beambefore the laser beam strikes the methane hydrate.
 13. The apparatus ofclaim 12, wherein the beam expander includes apparatus for forming anair curtain adjacent to a lens of the beam expander so that the lens isself-cleaning.
 14. The apparatus of claim 13, wherein the extractiontool includes an air passage for delivering air to the apparatus forforming an air curtain.
 15. The apparatus of claim 10, wherein the laseris a diode laser.
 16. The apparatus of claim 10, wherein the extractiontool includes a water cooling passage for cooling the optic fiber. 17.The apparatus of claim 10, wherein the extraction tool is supported by aplatform, which carries the laser.